The ideal method for non-invasive monitoring of biological or metabolic activity in the brainstem has not yet been established. Existing methods for evaluating cerebral tissue (e.g. PET) have limitations when applied to the brainstem. New noninvasive imaging methods are currently being studied. We are using MR perfusion, DEMRI, NMRS and PET to further investigate the imaging characteristics of pontine gliomas over time after radiation therapy. Response to treatment and tehrefore efficacy of new gents is typically measured using two-dimensional tumor measuyrements following WHO criteria, or more recently, using RECIST criteria. RECIST criteria have not been validated for the measurement of pediatric CNS tumors and two-dimensional measurements continue to be the standard in consortium trials. We compared the 1D, 2D and 3D measurements of diffuse intrinsic pontine gliomas by four separate blinded readers. The results show that there is significant variability (0-197%) in all measurements and change in tumor size is therefore a poor indicator of response for clinical trials. We have also electronically surveyed pediatric oncologists and neuro-oncologists across teh country to determine the standard practice of tumor measurement. Our results show that there is no standard measurement method being used in the measurement of these lesions. We are continuing to evaluate the utility of additional MR sequences, including perfusion and spectroscopic imaging.